No problems here so far with AJA io and FCP 4.5. New QT allows you to select multiple Audio inputs for recording but I haven’t fully tested yet. The HiDef material on Apple’s QT site is astonishing. The H264 codec is pretty amazing and HiDef material on a normal DVD is definitely viable; I now understand the thrust of DVD Studio 4. QT7 also allows simple capture from the AJA io but the interface is clunky and is more set up for working with iSight etc. I would be easy I suspect for a developer to make a very quick and easy capture app for video which simply wasn’t the case before QT7. I think we are going to see an explosion of little apps that exploit CoreVideo and CoreGraphics.
I’ve captured to FCP and layed back without problem using firmware 21-26; the new 22-27 firmware is still unstable IMHO.